Throttle-valve assembly

ABSTRACT

A throttle-valve assembly ( 10 ) having a housing ( 12 ), which has a continuous throttle opening ( 16 ) through which a gaseous medium ( 62 ) can flow in a main flow direction ( 60 ), in which a throttle valve ( 20 ) fastened pivotably on a throttle-valve shaft ( 18 ) is arranged in the throttle opening ( 16 ), and the throttle-valve shaft ( 18 ) can be pivoted by an actuator ( 26 ) arranged in the housing ( 12 ), in which, starting from the axis of rotation ( 19 ) of the throttle-valve shaft ( 18 ) downstream along the main flow direction ( 60 ) of the gaseous medium ( 62 ), the throttle opening ( 16 ) has an approximately straight cylinder section ( 64 ) with a height H 1  and a radius R Z  and in which a spherical-cap section ( 68 ) adjoins the approximately straight cylinder section ( 64 ). To reliably ensure a finely graduated control of the gaseous medium ( 62 ) passing through the throttle opening ( 16 ) during operation of the throttle-valve assembly ( 10 ), the spherical-cap section ( 68 ) has a central point ( 80 ) which, starting from the axis of rotation ( 19 ) of the throttle-valve shaft ( 18 ) downstream along the main flow direction ( 60 ) of the gaseous medium ( 62 ), is displaced by a distance H 2 , with the spherical-cap section ( 68 ) having a radius R K  which is approximately determined by the following equation: 
     
       
           R   K   =[R   Z   2 +( H   1   −H   2 ) 2 ] K .

FIELD AND BACKGROUND OF THE INVENTION

The invention relates to a throttle-valve assembly having a housing,which has a continuous throttle opening through which a gaseous mediumcan flow in a main flow direction, in which a throttle valve fastenedpivotably on a throttle-valve shaft is arranged in the throttle opening,in which the throttle-valve shaft can be pivoted by an actuator arrangedin the housing, in which, starting from the axis of rotation of thethrottle-valve shaft downstream along the main flow direction of thegaseous medium, the throttle opening has an approximately straightcylinder section with a height H₁ and a radius R_(Z) and in which aspherical-cap section adjoins the approximately straight cylindersection.

To control the quantity of fresh gas for a motor vehicle, use isgenerally made of throttle-valve assemblies. Throttle-valve assembliescomprise a housing having a throttle opening and a throttle elementarranged in the throttle opening. The throttle element assumes a certainposition in the throttle opening to allow through a certain quantity offresh gas. For this purpose, the throttle element can be activatedmechanically or electronically.

Housings of throttle-valve assemblies are generally produced fromplastic or metal. Housings of throttle-valve assemblies which aremanufactured from metal, for example, aluminum, may have particularlylow tolerances. Low tolerances are necessary for a throttle-valveassembly, in the region of the throttle valve, particularly if theintention is for the quantity of flow medium passing through thethrottle opening of the throttle-valve assembly to be able to beinfluenced even by a particularly small movement of the throttle valve.In the closing region of the throttle valve, these requirements are alsoreferred to as leakage-air requirements. However, metal housings ofthrottle-valve assemblies have the disadvantage that, after the housinghas been produced, for example by die-casting, complicated re-machiningof the housing is required. For example, re-machining of housings madeof aluminum is necessary in order to ensure the functional requirementsprovided in and on the housing. Functional requirements are, inparticular, the flow passage, the holder for the actuator and gear axisspacings. Precise machining of the bearing seats is also usuallynecessary, since the correct operating play (bearing clearance) isproduced only by the press fit on the needle bearing.

Throttle-valve assembly housings manufactured from plastic have a lowerweight than throttle-valve assembly housings which are manufacturedessentially from metal, in particular aluminum. Furthermore, plastic, asthe material, can also be adapted in an especially simple manner to awide variety of geometric configurations of the housing. Moreover, inthe case of plastic housings produced by injection molding, inserts, forexample bearings for mounting the throttle-valve shaft, can be placedinto the injection mold provided for the housing and encapsulated withplastic.

The throttle opening of a throttle-valve assembly usually has anapproximately cylindrical cross section. The approximately cylindricalcross section of the throttle opening has the effect of causing acontinuous increase in the quantity of flow medium flowing through overthe working range of the throttle valve when the throttle valve isopened. This may prove disadvantageous if the throttle valve and thethrottle opening have a particularly large diameter, for example 90 mmor more. This is because, from a certain opening angle of the throttlevalve, the mass of flow medium passing through the throttle opening onlychanges to a particularly small extent per unit of time, in particularat a particularly large diameter of the throttle valve, when theposition of the throttle valve changes, which means that a finelygraduated control of the power of the motor vehicle is no longerpossible from a certain opening angle of the throttle valve.

SUMMARY OF THE INVENTION

The invention is therefore based on the object of specifying athrottle-valve assembly of the type mentioned above, which reliablyensures a finely graduated control of the medium passing through thethrottle opening during operation of the throttle-valve assembly, inparticular for throttle valves having a particularly large diameter.

According to the invention, this object is achieved by virtue of thefact that the spherical-cap section has a central point which, startingfrom the axis of rotation of the throttle-valve shaft downstream alongthe main flow direction of the gaseous medium, is displaced by adistance H₂, with the spherical-cap section having a radius R_(K) whichis approximately determined by the following equation:

R _(K) =[R _(Z) ²+(H ₁ −H ₂)²]^(1/2).

The invention starts from the consideration that a throttle-valveassembly which reliably ensures a finely graduated control of the mediumpassing through the throttle opening during operation of thethrottle-valve assembly, in particular for throttle valves having aparticularly large diameter, is to be manufactured with a particularlylow outlay on production. The throttle valve is therefore to remainunchanged in its shape and design in order, for cost reasons, to be ableto continue installing standard throttle valves in the throttle-valveassembly. Since the housing of a throttle-valve assembly is usuallyadapted to specific installation requirements, a finely graduatedcontrol of the medium passing through the throttle opening duringoperation of the throttle-valve assembly is to be reliably ensured bymeans of a special shaping of the throttle opening. In addition to thesimple cylinder shape of the throttle opening, a spherical cap can beimpressed in a particularly simple manner into the throttle opening of athrottle-valve assembly. The radius of the spherical cap and distance ofthe central point of the spherical cap from the central point of thethrottle-valve shaft are available in this case as parameters for thedesign of the spherical cap. Extensive considerations and calculationshave led to the surprising result that displacement of the central pointof the spherical cap relative to the central point of the throttle-valveshaft linked to a requirement for the radius of the spherical cap hasthe effect of reliably ensuring a sensitive control of the mediumpassing through the throttle opening even for throttle valves having aparticularly large diameter.

Starting from the axis of rotation of the throttle-valve shaft upstreamcounter to the main flow direction of the gaseous medium, the throttleopening advantageously has an approximately straight cylinder sectionwith a height G₁ and a radius P_(Z), with a spherical cap sectionadjoining the approximately straight cylinder section, the spherical-capsection having a central point which, starting from the axis of rotationof the throttle-valve shaft upstream along the main flow direction ofthe gaseous medium, is displaced by a distance G₂, with thespherical-cap section having a radius P_(K) which is approximatelydetermined by the following equation:

P _(K) =[P _(Z) ²+(G ₁ −G ₂)²]^(1/2).

The characteristic curve along the throttle-valve assembly canadditionally be flattened by the fact that the throttle opening has aspherical-cap section both downstream and upstream of the axis ofrotation of the throttle-valve shaft, the radius of both spherical capsbeing spaced apart from the central point of the throttle-valve shaftand the radius of the spherical caps satisfying at least one of theequations stated above.

In an advantageous manner, the value of R_(Z) is equal to the value ofP_(Z) and the value of R_(K) is equal to the value of P_(K). A throttleopening of a throttle-valve assembly, which opening is constructedsymmetrically relative to the closed position of the throttle valve, canbe produced with particularly little outlay. In this case, theparameters H₁, H₂ and R_(Z) can be used to adapt the particularthrottle-valve assembly to specific requirements of the particular motorvehicle.

The housing is advantageously produced by injection molding and ispredominantly made of plastic, with at least the straight cylindersection in the region of movement of the throttle valve being formed bya metal insert injected into the housing. A metal insert for a plastichousing can be manufactured with smaller tolerances than is possible fora housing made of plastic. Therefore, in order to obtain a predeterminedcharacteristic, a throttle opening which is formed from metal standsout. In order, however, at the same time, to ensure a throttle openinghaving particularly small tolerances and a particularly low weight ofthe throttle-valve assembly, only the region of the throttle openingrelevant to the characteristic curve is manufactured from metal, theremaining region of the housing being made predominantly or completelyof plastic.

The spherical-cap section is advantageously formed by a metal insertintegrated in the housing. By this means, an individual spherical-capshape can be realized with a particularly low outlay for each type ofthrottle-valve assembly.

Both the cylinder section and the spherical-cap section areadvantageously formed by a single-piece metal insert. As a result,sealing problems between the approximately straight cylinder section inthe region of movement of the throttle valve and the spherical-capsection do not occur. Moreover, unevennesses in the boundary regionbetween the approximately straight cylinder section in the region ofmovement of the throttle valve and the spherical-cap section couldresult in swirling of the gaseous medium passing through the throttleopening during operation of the throttle-valve assembly, which couldhave a negative effect on the characteristic curve of the throttlevalve.

The metal insert is advantageously constructed so as to hold thebearings of the throttle-valve shaft. As a result, the bearings areintegrated in the mechanical stability of the metal insert. Thisarrangement of the bearings enables the throttle-valve shaft to bemounted in a particularly stable manner in the metal insert.

A position detection device is advantageously provided for thethrottle-valve shaft, a holder being integrated in the metal insert forthe position detection device. In this case, the mechanical stability ofthe metal insert ensures that the position detection device isparticularly securely held in the housing of the throttle-valveassembly. At the same time, the position detection device canadditionally be pre-adjusted relative to the throttle-valve shaft viathe holder provided in the metal insert, as a result of which theposition detection device requires only a particularly small amount ofadjustment. In this case, the position detection device can be put intoplace even at the point at which the metal insert is integrated in thehousing.

The actuator is advantageously to be arranged on a base plate, the baseplate being constructed as a single piece with the metal insert. By thismeans, heat arising during operation of the actuator can be conductedaway to the metal insert via the base plate, with sufficient cooling ofthe metal insert being reliably ensured by the gaseous medium passingthrough the throttle opening.

The advantages obtained with the invention reside, in particular, in thefact that a characteristic curve for a throttle-valve assembly can beobtained by a special shaping of the throttle opening in the region ofmovement of the throttle valve and not by a change in the shape of thethrottle valve and/or arrangement of the throttle-valve shaft, saidcharacteristic curve covering a range which has previously not beenachieved with known throttle-valve assemblies. This range of thecharacteristic curves for a throttle-valve assembly that has beenacquired by the invention is advantageous in particular in the case ofthrottle valves having a particularly large diameter, so that thelatter, in spite of their size, reliably ensure a particularly finelygraduated control of the power of the internal combustion engine.

BRIEF DESCRIPTION OF THE DRAWINGS

An exemplary embodiment of the invention will be explained in greaterdetail with reference to a drawing, in which:

FIG. 1 shows a diagram of a throttle-valve assembly,

FIG. 2 shows a diagram of a section through the throttle-valve assemblyaccording to FIG. 1,

FIG. 3 shows a diagram of a section through the throttle opening in theregion of the throttle valve, and

FIG. 4 shows an overview of characteristic curves of variousthrottle-valve assemblies.

Parts corresponding to one another are provided with the same referencenumbers in all of the figures.

DETAILED DESCRIPTION OP THE PREFERRED EMBODIMENT

The throttle-valve assembly 10 according to FIG. 1 is used to feed airor a fuel/air mixture to a consumer (not illustrated), for example aninjection device of a motor vehicle (likewise not illustrated), it beingpossible to control the quantity of fresh air to be fed to the consumerby means of the throttle-valve assembly 10. For this purpose, thethrottle-valve assembly 10 has a housing 12 which is manufacturedpredominantly from plastic 14 and has been produced by injectionmolding. As an alternative, however, the housing 12 can also bemanufactured entirely from metal, in particular aluminum. The housing 12has a throttle opening 16 via which the air or a fuel/air mixture can befed to the consumer (not illustrated). To allow the volume of fresh gasto be fed in to be adjusted, a throttle valve 20 is arranged on athrottle-valve shaft 18. Rotating the throttle-valve shaft 18 about itsaxis of rotation 19 simultaneously pivots the throttle valve 20 arrangedon the throttle-valve shaft 18, as a result of which the active crosssection of the throttle opening 16 is enlarged or reduced. Thethroughput of the air or fuel/air mixture through the throttle opening16 of the throttle-valve assembly 10 is thus regulated by means of anincrease or reduction in the active cross section of the throttleopening 16 by the throttle valve 20.

The throttle-valve shaft 18 can be connected to a cable pulley (notillustrated specifically), which, in turn, is connected by a Bowdencable to an adjusting device for a power demand. In this context, theadjusting device can be constructed as an accelerator pedal of a motorvehicle, actuation of this adjusting device by the driver of the motorvehicle thus enabling the throttle valve 20 to be moved from a positionof minimum opening, in particular a closed position, as far as aposition of maximum opening, in particular an open position, in orderthereby to control the power output of the motor vehicle.

In contrast, it is possible either for the throttle-valve shaft 18(shown in FIG. 1) of the throttle valve assembly 10 to be adjusted by anactuator over part of the range and otherwise by means of theaccelerator pedal or for the throttle valve 10 to be adjusted over theentire range of adjustment by an actuator. In these “electronic engineoutput control” or “drive-by-wire” systems, mechanical power control,for example depressing an accelerator pedal, is converted into anelectric signal. This signal, in turn, is fed to a control unit, whichproduces an activation signal for the actuator. In these systems, thereis no mechanical coupling between the accelerator pedal and the throttlevalve 20 in normal operation.

To adjust the throttle-valve shaft 18 and hence the throttle valve 20,the throttle-valve assembly 10 therefore has a drive housing 22 and agear housing 24. The drive housing 22 and the gear housing 24 areconstructed as a single piece with the housing 12 of the throttle-valveassembly 10, but they may also overall form a separate, single-piececonstructional unit or else each can be constructed as a single piece byitself.

An actuator 26 constructed as an electric motor is arranged in the drivehousing 22. The actuator 26 constructed as an electric motor moves thethrottle-valve shaft 18 via a reduction gear arranged in the gearhousing 24. The reduction gear is not illustrated specifically in thedrawing. The actuator 26 is connected in a manner not illustratedspecifically to a power source arranged outside the throttle-valveassembly 10 and to a control unit. The control unit transmits to theactuator a signal, by means of which the actuator 26 brings about acertain position of the throttle-valve shaft 18 via the reduction gear.The actual position of the throttle-valve shaft 18 can be detected via aposition detection device 28 which is constructed as a potentiometer andin which the slider of the potentiometer is connected to thethrottle-valve shaft 18.

Furthermore, the throttle-valve assembly 10 according to FIG. 1comprises a metal insert 30 which is manufactured from metal 32 which isin the form of aluminum. The metal insert 30 has been placed into aninjection mold provided for the housing 12 of the throttle-valveassembly 10 and has been encapsulated with plastic 14. In this case, theregion of the metal insert 30 that forms the throttle opening 16 has notbeen covered by plastic, with the result that, in the region of thethrottle opening, the metal 32, which is in the form of aluminum, formsthe throttle opening 16.

The metal insert 30 is formed as a single piece with an end shield orbase plate 34 on which the actuator 36, which is constructed as anelectric motor, is arranged. By this means, heat arising duringoperation of the actuator 26 can be conducted away to the throttleopening 16 via the metal insert 30. Furthermore, the metal insert 30 hasa holder 36 on which the position detection device 28, which isconstructed as a potentiometer, for the throttle-valve shaft 18 isarranged. The holder 36, which is constructed as a single piece with themetal insert 30, enables the adjustment of the position detection device28 constructed as a potentiometer to be particularly simple, since theposition of the position detection device 28 relative to thethrottle-valve shaft 18 is predetermined by the metal insert 30.

The metal insert 30 has two leadthroughs 38 each having an extension 40.The two extensions 40 are provided for holding bearings 42 for thethrottle-valve shaft 18. The housing 12 of the throttle-valve assembly10 has proven particularly installation-friendly for this, since, afterthe housing 12 has been constructed, the bearings 42 have simply to beinserted into the extensions 40 provided for this purpose.

On the one side—on the left-hand side according to FIG. 1—thethrottle-valve shaft 18 ends in a space 44 in which so-called returnsprings and/or emergency-running springs can be accommodated, forexample. The return springs and/or emergency-running springs preload thethrottle-valve shaft in the closing direction, with the result that theactuator 26 acts against the force of the return springs and/oremergency-running springs. A so-called emergency-running spring has theeffect of moving the throttle valve 20 into a defined position if theactuator fails, this position generally being above the idling speed. Asan alternative or in addition, the throttle-valve shaft 18 can alsoproject out of the housing 12 of the throttle-valve assembly 10 beyondthe space 44. It is then possible for a cable pulley (not illustrated inthe drawing), for example, to be mounted at the end of thethrottle-valve shaft 18 which is connected to an accelerator pedal via aBowden cable, thus providing a mechanical desired-value input. Thismechanical coupling of the throttle-valve shaft 18 with the acceleratorpedal (not illustrated specifically in the drawing) can ensure that thethrottle-valve assembly 10 operates in emergency situations, for exampleif the actuator 26 fails. The end of the space 44 that is remote fromthe end of the extension 14 can be used for holding further elements.Furthermore, further attachments can be arranged on the end face of theextensions 40, said attachments being provided for holding additionalelements, such as, for example, web shafts for gear wheels or segmentgears belonging to the gear (not shown).

The housing 12 of the throttle-valve assembly 10 can be closed by ahousing cover 50. For this purpose, the housing 12 of the throttle-valveassembly 10 has a peripheral flat 52 in the direction of the housingcover 50, said flat corresponding to a peripheral web 54 on the housingcover 50. The flat 52 and the web 54 ensure a well-defined position ofthe housing cover 50 on the housing 12. After the housing cover 50 isplaced onto the housing 12, the two mutually facing faces of the flat 52and of the web 54 are fused together by a laser beam, thus producing avirtually unreleasable connection. As an alternative, however, thehousing cover 50 may also be bonded onto the housing 12. Furthermore,the housing 12 has flange lugs 56 for connection to elements which arearranged outside the throttle-valve assembly 10 and are constructed as asingle piece with the housing 12.

FIG. 2 shows a diagram in longitudinal section of the throttle-valveassembly 10 according to FIG. 1. According to FIG. 2, the metal insert30 is manufactured from aluminum. The metal insert 30 forms a subregionof the throttle opening 16 through which a gaseous medium 62 can flow ina main flow direction 60. In the region of the closed position of thethrottle valve 20 both downstream and upstream of the main flowdirection 60 of the gaseous medium 62, the metal insert 30 in each casecomprises a straight cylinder section 64 and 66. The straight cylindersections 64 and 66 are constructed as a single piece, but mayalternatively also be constructed as two pieces. The straight cylindersections 64 and 66 are adjoined in each case by a spherical-cap section68 and 70, respectively. The spherical-cap sections 68 and 70 areconstructed as a single piece with the straight cylinder sections 64 and66. Thus, in a single-piece embodiment, the metal insert 30 comprisesthe two straight cylinder sections 64 and 66 and the two spherical-capsections 68 and 70. As an alternative, however, the straight cylindersections 64 and 66 and the spherical-cap sections 68 and 70 can also beconstructed in each case as a single piece or can be constructed as asingle piece in pairs. The outer circumference of the metal insert 30and at least part of its end faces are surrounded by the plastic 14 ofthe housing 12.

FIG. 3 shows the parameters of the metal insert 30 in the region of thethrottle-valve shaft 18. Starting from the axis of rotation 19 of thethrottle valve shaft 18, the approximately straight cylinder section 64of the metal insert 30 extends downstream of the main flow direction 60of the gaseous medium 62 with a height H₁. In this region, the metalinsert 30 has a radius R_(Z). The approximately straight cylindersection 64 of the throttle opening 16 with the height H₁ is adjoined,starting from the axis of rotation 19 of the throttle-valve shaft 18upstream counter to the main flow direction 60 of the gaseous medium 62by a likewise approximately straight cylinder section 66 of the metalinsert 30 with a height G₁. Downstream along the main flow direction 60of the gaseous medium 62, the first, approximately straight cylindersection 64 of the metal insert 30 is adjoined by a spherical-cap section68. The central point 80 of the spherical-cap section 68 does not lie inthe imaginary central point 82 of the throttle-valve shaft 18. Thecentral point of the spherical-cap section 68 is displaced from theimaginary central point 82 of the throttle-valve shaft 18 by an amountH₂. The spherical-cap section 68 has a radius which satisfies thefollowing equation:

R _(K) =[R _(Z) ²+(H ₁ −H ₂)²]^(1/2).

Upstream counter to the main flow direction 60 of the gaseous medium 62,the second, approximately straight cylinder section 66 is likewiseadjoined by a spherical-cap section 70. The second spherical-cap section70 also has a central point 84 which is displaced from the imaginarycentral point 80 of the throttle-valve shaft 18 by an amount G₂. Theradius of the spherical-cap section 70 is defined by the followingequation:

P _(K) =[P _(Z) ²+(G ₁ −G ₂)²]^(1/2) ₂.

In this exemplary embodiment, the value of R_(Z) is equal to the valueof P_(Z) and the value of R_(K) is equal to the value of P_(K). As analternative, however, the values may also be different or only some ofthem may be the same.

The graph according to FIG. 4 illustrates the effects of the parametersof the metal insert 30 in the region of movement of the throttle-valveshaft. On the graph, the working region 90 of the throttle-valve shaft18 is indicated on the abscissa in percent (%) and the mass 92 ofgaseous medium passing through the throttle opening 16 is indicated onthe ordinate in percent (%). The characteristic curve I ischaracteristic for a throttle-valve assembly which has an approximatelycylindrical throttle opening. The characteristic curve II corresponds toa throttle-valve assembly, in which the throttle opening has, bothupstream and downstream in the region of the throttle-valve shaft, acylinder section which is adjoined in each case, i.e. both upstream anddownstream, by a spherical-cap section. In this case, the central pointof the spherical cap lies on the edge of the respective, cylindricalsection in alignment with the imaginary central point of thethrottle-valve shaft. The characteristic curve III corresponds to athrottle-valve assembly, in which the throttle opening has, in theregion of the throttle-valve shaft, a cylindrical section both upstreamand downstream of the main flow direction 60 of the gaseous medium 62.The straight cylinder section is adjoined both upstream and downstreamby a respective spherical-cap section. In this case, the spherical-capsection has a central point which coincides with the imaginary centralpoint of the throttle-valve shaft.

In contrast to this, the throttle-valve assembly 10 according to FIGS. 1to 3 has a metal cap 30 which has, both upstream and downstream of themain flow direction 60 of the gaseous medium 62 starting from the axisof rotation 19 of the throttle-valve shaft 18, a straight cylindersection 64 and 66, respectively. The two straight cylinder sections 64and 66 are adjoined in each case by the spherical-cap sections 68 and70. In this case, the radius of the spherical-cap sections 68 and 70 isspaced apart from the imaginary central point of the throttle-valveshaft 18. The radius of the spherical-cap sections 68 and 70 satisfiesat least one of the equations stated above. The graph according to FIG.4 clearly shows that the characteristic curve IV which lies outside thehitherto customary regions of the characteristic curves can be achievedby the throttle-valve assembly 10 according to FIGS. 1 to 3. Thisreliably ensures a finely graduated control of the gaseous medium 62passing through the throttle opening 16 even for throttle valves havinga particularly large diameter.

I claim:
 1. A throttle-valve assembly (10) having a housing (12), whichhas a continuous throttle opening (16) through which a gaseous medium(62) can flow in a main flow direction (60), the throttle valve assemblyfurther comprising: a throttle valve (20) fastened pivotably on athrottle-valve shaft (18) and being located in the throttle opening(16); an actuator (26) disposed in the housing (12) for pivoting thethrottle-valve shaft (18); wherein starting from an axis of rotation(19) of the throttle-valve shaft (18) downstream along the main flowdirection (60) of the gaseous medium (62), the throttle opening (16) hasan approximately straight cylinder section (64) with a height H₁ and aradius R_(Z), and wherein the throttle opening (16) includes aspherical-cap section (68) that adjoins the approximately straightcylinder section (64); the spherical-cap section (68) has a centralpoint (80) displaced from the axis of rotation (19) of thethrottle-valve shaft (18), downstream along the main flow direction (60)of the gaseous medium (62), by a distance H₂; and the spherical-capsection (68) has a radius R_(K) which is approximately determined by thefollowing equation: R _(X) =[R _(Z) ²+(H ₁ −H ₂)²]^(1/2).
 2. Thethrottle-valve assembly (10) as claimed in claim 1, wherein; proceedingfrom the axis of rotation (19) of the throttle-valve shaft (18) upstreamcounter to the main flow direction (60) of the gaseous medium (62), thethrottle opening (16) has an approximately straight cylinder section(66) with a height G₁ and a radius P_(Z); the straight cylinder section(64) is a first cylinder section, the spherical cap section (68) is afirst cap section, and the throttle valve assembly further comprises asecond spherical-cap section (70) which adjoins an approximatelystraight second cylinder section (66) located opposite the firstcylinder section, the second spherical-cap section (70) has a centralpoint (84) which, starting from the axis of rotation (19) of thethrottle-valve shaft (18), upstream along the main flow direction (60)of the gaseous medium (62), is displaced by a distance G₂ from the axisof rotation (19), with the second spherical-cap section (70) having aradius P_(K) which is approximately determined by the followingequation: P _(K) =[P _(Z) ²+(G ₁ −G ₂)²]^(1/2).
 3. The throttle-valveassembly (10) as claimed in claim 1, wherein the value of R_(Z) is equalto the value of P_(Z) and the value of R_(K) is equal to the value ofP_(K).
 4. The throttle-valve assembly (10) as claimed in claim 2,wherein the housing (12) is produced by injection molding and ispredominantly made of plastic (14), with at least either of the firstand the second straight cylinder section (64, 66) being formed by ametal insert (30) integrated in the housing (12).
 5. The throttle-valveassembly (10) as claimed in claim 2, wherein either of the first and thesecond spherical-cap sections (68, 70) is formed by a metal insert (30)integrated in the housing (12).
 6. The throttle-valve assembly (10) asclaimed in claim 5, wherein either of the first and the second straightcylinder sections (64, 66) and either of the first and the secondspherical-cap sections (68, 70) are formed by a single-piece metalinsert (30).
 7. The throttle-valve assembly (10) as claimed in claim 4,wherein the metal insert (30) is constructed so as to hold bearings (42)of the throttle-valve shaft (18).
 8. The throttle-valve assembly (10) asclaimed in claim 4, wherein the throttle-valve shaft (18) furthercomprises a position detection device (28) held in a holder (36) in themetal insert (30).
 9. The throttle-valve assembly (10) as claimed inclaim 4, wherein the actuator (26) is arranged on a base plate (34), thebase plate (34) being constructed as a single piece with the metalinsert (30).
 10. The throttle-valve assembly (11) as claimed in claim 2,wherein the value of R_(Z) is equal to the value of P_(Z) and the valueof R_(K) is equal to the value of P_(K).